Peaches, peas and potatoes, oh my! Weaning and introducing your baby to a wider range of foods can be fun (and messy!), but if your baby is under 6 months old and you’re getting ready to transition to solid foods, think again. While many store-bought purees and cereals are advertised as being good for babies as young as 4 months old, a new study shows that commercial baby foods do not offer the nutrients that babies need.

A team at the University of Glasgow’s School of Medicine tested 479 store-bought baby foods and found that all the ready-made, spoonable foods had the same energy content as breast milk, and offered only 40 percent more protein than formula milk. Study author Dr. Charlotte Wright says that her team did not find much of a nutritional difference between organic baby foods and the rest of the foods they tested.

What’s more, most of the commercial baby foods tested contained less nutrients than homemade food: babies would need to eat twice as much of the jarred baby foods to get the same energy and protein as meals cooked at home.

But even though homemade foods offer better nutrients, Dr. Wright says that if mothers are breastfeeding, they should avoid giving babies any food other than breast milk until they’re 6 months old, in keeping with the American Academy of Pediatrics guidelines for exclusive breastfeeding for the first 6 months after birth.

“Breast milk will be sufficient during that time and giving other foods and drinks carries two major risks,” says Wright. “Firstly, this will reduce the amount of breast milk the baby receives, since they will fill up on the other foods and thus lose the full protection against infection and other benefits they need from breast milk. Secondly, because they are taking less milk they will not stimulate the breast enough and then the supply of milk will gradually reduce and is likely to fail.”

Wright says that if mothers cannot breastfeed, then formula is the best alternative.

The other issue with commercial products is that they contain a lot of sugar, typically from fruit juices, which could encourage babies to develop a sweet tooth, which in turn might lead to tooth decay. “People might think that something sweetened with fruit is healthier, but it’s not,” says Dr. Wright. “Young babies like sweet food because it tastes like breast milk, but it is not moving them on.”